Study On The Performance Of New Negative Electrode Materials In Hybrid Electrochemical Capacitors

With the rapid development of the global economy, the depletion of fossil fuels and the deterioration of environmental pollution issues, there is an urgent need for clean,efficient and sustainable sources of energy, as well as new technologies associated with energy conversion and storage. The hybrid electrochemical capacitors, combining two different storage mechanisms of lithium-ion batteries and electric double layer capacitors,exhibit high energy density and long cycling life, and become promising energy storage devices for electric vehicles and hybrid electric vehicles. The electrode material is one of the most critical factors affecting the performance of the energy storage devices. Thus, a major focus of electrochemical capacitors research should be to find new electrode materials with high specific capacitance and excellent rate performance.Niobium nitride/nitrogen-doped graphene hybrid materials were prepared by a simple hydrothermal method combined with ammonia annealing. It was found that the as-obtained niobium nitride nanoparticles were about 10-15 nm in size and homogeneously anchored on graphene nanosheets. A non-aqueous lithium-ion capacitor was fabricated with activated carbon(AC) cathode and the niobium nitride/nitrogen-doped graphene anode, which delivered high energy densities of98.4-122.7 W h kg-1 at power densities of 100-2000 W kg-1, respectively. The capacity retention was 81.7% after 1000 cycles at a current density of 500 mA g-1. The high energy and power of this hybrid capacitor bridges the gap between conventional high specific energy lithium-ion batteries and high specific power electrochemical capacitors, which holds great potential applications in energy storage for hybrid electric vehicles.Hybrid sodium-ion capacitors(NICs) have tremendous potential in large-scale energy storage applications due to their low cost, high power and long lifetime. However,it remains a great challenge to find desirable anode materials with fast kinetics and superior cycle life. Two-dimensional(2D) transition metal dichalcogenide nanosheet is attracting increasing attentions in energy storage due to unique nanoconstruction and electronic properties. Here, molybdenum disulfide(Mo S2) was adopted as a negative electrode material for the asymmetric electrochemical capacitors of Mo S2//AC using Na+-based organic electrolytes. The electrochemical performance tests revealed that the NICs had relatively high energy density and power density, i.e., 110.7 W h kg-1 and 2500 W kg-1, respectively. The hybrid capacitors also showed good cycle stability, displaying a capacity retention of 86.1% after 1000 cycles at current density of 2 A g-1.